1. Field of the Invention
The present invention is broadly concerned with improved clamps used for clamping workpieces to fixtures, and especially so-called swing clamps which simultaneously move in axial and rotational directions to allow easy placement and removal of workpieces. More particularly, the invention is concerned with such clamps including a shiftable piston equipped with a workpiece-engaging outer head, where piston movement is guided and controlled via an internal cam assembly made up of a specially configured cam track and cam follower ball arrangement. Such cam assemblies are provided with spring units serving to bias and self-center the follower balls into the associated tracks, providing many operational advantages including increased clamp speeds and reduction in clamp wear and damage.
2. Description of the Prior Art
Hydraulic clamps are commonly used in manufacturing operations to hold and clamp workpieces to stationary fixtures, so that the workpieces may be machined or otherwise worked upon. Typical hydraulic clamps include a cylinder body adapted for attachment to a fixture and a piston telescopically received within the cylinder body for movement between an retracted, clamping position and an extended, release position. A clamping head is attached to the distal end of the piston for holding and clamping workpieces to the fixture when the piston is in its retracted, clamping position. Commonly, several such clamps are mounted to a single fixture so that a workpiece may be securely held at several locations while it is being worked upon.
Swing clamps are hydraulic clamps that include swinging mechanisms serving to swing the clamping heads away from the workpiece when the pistons are extended to their release positions. Swing clamps make it easier to load and unload workpieces from fixtures, especially in confined spaces.
One type of swinging mechanism used in swing clamps is a cam assembly having a curved cam track or groove formed in either the piston or the cylinder body and a corresponding cam follower ball attached to the other of the piston and cylinder body. The follower ball moves along the curved cam track when the piston is shifted which serves to rotate the piston and clamping head as described.
Conventional cam assemblies in swing clamps are subject to premature wear over time that interferes with the swinging operation of the clamps. Specifically, when the cam follower ball moves in the track, it is subject to circumferential forces tending to push the ball to the sides of the groove. Over time, the cam ball wears down the edges of the track and creates dimples along the length thereof. The dimples and worn regions of the cam track often catch the ball during piston movement, creating a “choppy” clamp operation. When a clamp is used in severe conditions, its cam ball may completely wear down the edges of the track, causing the ball to completely roll out of the groove.
Excessive wear on the cam grooves of a clamp can be a serious problem. In many clamping operations, it is important for the clamping head to swing to a precise location away from the workpiece, and then return to the same exact starting position when the clamp is shifted to its clamping position. When the cam groove on a clamp become worn, the swing clamp can no longer achieve this precise and repeatable swinging movement. Thus, the entire swing clamp must be replaced, even though the remaining parts of the clamp are in good condition.
U.S. Pat. No. 5,820,118 describes a decided improvement in the swing clamp art. In this patent, uses may of a special cam track design which inhibits the cam follower ball from prematurely wearing the cam track edges. Specifically, the cam track described in the '118 patent includes a central arcuate region and a pair of substantially planar side faces extending tangentially from the central arcuate region. This construction forces the cam follower ball to be more centrally seated within the cam track without pushing up against the edges of the cam track.